From the day the Pilgrims stepped off the Mayflower, religion has played a prominent role in American public life. The faithful have been vital participants in nearly every major social movement in U.S. history, progressive as well as conservative. Still, the close intertwining of religion and politics in the last 40 years is unusual, especially in the degree of the politicization of religion itself. Indeed, religion's influence on U.S. politics has hit a high-water mark, especially on the right. Yet at the same time, its role in Americans' personal lives is ebbing. As religion and politics have become entangled, many Americans, especially younger ones, have pulled away from religion. And that correlation turns out to be causal, not coincidental.

It is no surprise that religion and politics should be connected to some degree in a highly religious and democratic nation. In the nineteenth century, U.S. political parties were divided along sectarian lines: pietistic versus liturgical, low church versus high church, Protestant versus Catholic. But whereas the past saw partisans of different religions (often with an ethnic tinge) face off in the political arena, today partisan divisions are not defined by denomination; rather, they pit religiously devout conservatives against secular progressives. Moreover, to a degree not seen since at least the 1850s (and perhaps not even then), religious mobilization is now tied directly to party politics.

In fact, over the last 20 years, church attendance has become the main dividing line between Republican and Democratic voters. (African Americans are a sharp, but singular, exception; although most Democratic voters are now secular, African Americans, the most loyal Democrats, are also the most religious group in the United States.) The so-called God gap, between churchgoing Republicans and secular white Democrats, rose sharply throughout the 1990s and early years of this century. Before the 2008 presidential election, one team of consultants even specialized in teaching Democratic candidates how to "do God," so they could eat into the Republicans' support among religious Americans. Yet in 2008, the God gap remained as wide as ever: according to data we collected, among whites, 67 percent of weekly churchgoers voted for Senator John McCain, as compared with 26 percent of those who never attended church.

The connection between religiosity and political conservatism has become so deeply embedded in contemporary U.S. culture that it is startling to recall just how new the alignment is. In the 1960s, churchgoers were actually more likely than nonchurchgoers to be Democrats. Into the 1980s, there were still plenty of progressives in the pews on Sunday morning and plenty of conservatives who stayed home. The rather sudden shift since then has, and will have, both short-term and long-term implications for both politics and religion. For now, Republicans must seek to appease their fervently religious base without alienating a general electorate that increasingly finds the mixture of religion and politics distasteful. In the long run, the trend could undermine the historic role of religion in the United States, as younger generations reject organized religion itself. The country has arrived at today's close nexus between religion and partisanship only recently, and understanding how it got there -- and how the role of religion in the United States has changed in recent decades -- will help explain where it might be headed.

IN THE BEGINNING

To get a better sense of how novel the present political-religious landscape is, we must go back to the 1950s. That decade was highly religious; indeed, some historians argue that it was the most religious in all of American history. Of course, there are many ways to gauge national trends in religiosity, but for decades, one Gallup poll question, "Is religion's influence on American life increasing or decreasing?" has proved a finely tuned seismometer of religious tremors. In 1957, 69 percent of those Americans surveyed told Gallup that they thought the influence of religion in American life was on the rise. Only 14 percent said it was declining. Every objective measure indicates that they were right: more Americans than ever were attending religious services, more churches were being built to accommodate them, and more books of Scripture were being sold and read. But in President Dwight Eisenhower's America, religion had no partisan overtones. Ike was as popular among those who never darkened the door of a church (or synagogue, and so on) as among churchgoers.

Then came the 1960s, and a dramatic turn in attitudes toward authority and especially toward conventional sexual morality, an issue tightly connected to religious belief. In just four years, between 1969 and 1973, the percentage of Americans who approved of premarital sex doubled, from one-fourth to one-half. That increase was stunning and almost entirely concentrated among the baby boomers, who were then coming of age. By 1970, fully 75 percent of Americans surveyed concluded that religion's influence in American life was waning. Collapsing church attendance confirmed their view. Yet even then, religiosity did not skew more to the right than the left; neither during the religious boom of the 1950s nor in the religious bust of the 1960s was religion linked to partisan politics.

Nor did the 1960s put the United States on an inexorable path toward secularism. Far from it: instead, among more conservative Americans, the moral earthquake triggered a return to religion, or at least a particular type of religion. Beginning in the mid-1970s, in an aftershock to the 1960s, conservative forms of religion, especially evangelical Protestantism, expanded. At the same time as liberal Protestantism and churchgoing Catholicism were virtually collapsing, many Americans who sought a reaffirmation of traditional norms, especially when it came to sex and "family values," found what they were looking for in evangelical Protestantism. The new evangelicals also broke free of the self-imposed cultural exile of their fundamentalist forebears. They did not shun a sinful world but instead sought to change it, including its politics.

An early harbinger of evangelicalism's new political role was the 1976 presidential campaign of the Democrat Jimmy Carter, who spoke openly of himself as a "born-again Christian," a label once unthinkable in mainstream U.S. politics. At the other end of the political spectrum, meanwhile, moral conservatives banded together to fight the Equal Rights Amendment, gay rights, and abortion. Evangelicalism began morphing from a purely religious movement into a political one that allied devout Americans from many denominations, including Catholics and Mormons. Once more, Gallup's seismometer noted the increasing prominence of religion. In 1976, it registered that 44 percent of respondents thought religion was gaining influence, and 45 percent thought it was losing influence.

Then, in his 1980 presidential campaign, the Republican Ronald Reagan actively courted the religious vote with considerable success. Unlike Eisenhower in the 1950s or even Presidents Richard Nixon and Gerald Ford in the 1970s, Reagan and the Republican presidential candidates that followed him began to pick up the support of formerly Democratic evangelicals in the South and observant Catholics in the North.

The first aftershock to the 1960s thus had two components: one religious (the rise of evangelicals) and the other political (the rise of the religious right). The political movement continues, but the religious dimension ended in the early 1990s. As a fraction of the total population (and, even more dramatically, as a fraction of Americans under 30), the number of evangelicals has been declining for nearly 20 years and is back to where it was at the beginning of the 1970s.

Although many of the political organizations associated with the religious right, such as the Moral Majority and the Christian Coalition, have disappeared or faded into near irrelevance, their legacy remains strong: a Republican activist base that advocates both moral traditionalism and a greater role for religion in the public square.

The rise of the religious right echoes in some respects a common theme in U.S. history. Most major social movements, both progressive and conservative, have included important religious themes: "the right to life" and "family values" today, abolitionism and prohibition yesterday. But today's unusually intimate ties between organized religion and one particular political party have had unintended consequences for both politics and religion.

THE GOD-GIVEN RIGHT

With the rise of the religious right came the much-discussed God gap between Republicans and Democrats. Each year, fewer and fewer Americans identify as secular Republicans or religious Democrats. What happened to those who once did? Did they adjust their politics to fit their religion, or vice versa? Surprisingly, politics has mostly determined religious practice. Formerly religious Democrats (except among African Americans) have drifted away from church, and formerly unobservant Republicans have found religion.

Take the Tea Party. Even this ostensibly secular movement has strong religious undertones. A large, nationally representative survey that we first conducted in 2006 (before the Tea Party was formed) and repeated with the same respondents in 2011 casts doubt on the conventional wisdom about the movement's origin. In its early days, the Tea Party was often described as comprising nonpartisan political neophytes who, hurt by the Great Recession, had been spurred into action out of concern over runaway government spending. This is a triple myth. In reality, those Americans who support the Tea Party were (and remain) overwhelmingly partisan Republicans. They were politically active even in the pre-Tea Party days, and they were no more likely than anyone else to have suffered hardship during the recent economic downturn.

Indeed, it turns out that the strongest predictor of a Republican becoming a Tea Party supporter is whether he or she evinced a desire in our 2006 survey to see religion play a prominent role in politics. And that desire does not simply reflect members' high religiosity. Tea Partiers are, on average, more religiously observant than the typical American, but not more so than other Republicans. Rather, they are distinctively comfortable blending religion and politics. Tea Partiers are more likely than other Republicans to say that U.S. laws and policies would be better if the country had more "deeply religious" elected officials, that it is appropriate for religious leaders to engage in political persuasion, and that religion should be brought into public debates over political issues. The Tea Party's generals might say that their overriding concern is smaller government, but the rank and file is after a godlier government.

Tea Partiers' views in this respect are increasingly out of step with those of most Americans. According to Gallup polls, as early as 1984, just as the alliance between religious and political conservatives was crystallizing, most Americans opposed the idea of religious groups campaigning against specific candidates. Moreover, according to the widely respected national General Social Survey, as the public visibility of the religious right increased between 1991 and 2008, growing numbers of Americans expressed the conviction that religious leaders should not try to influence people's votes or government decisions. In 1991, 22 percent of those surveyed said they "strongly agree" that religious leaders should not try to influence government decisions; by 2008, that figure had nearly doubled, to 38 percent. In our 2011 survey, 80 percent of respondents said that it is not proper for religious leaders to tell people how to vote, and 70 percent said that religion should be "kept out of public debates over social and political issues."

It should thus come as no surprise that many Americans have negative views of the Tea Party. In the same 2011 poll, the Tea Party ranked at the bottom of a list of two dozen U.S. religious, political, and racial groups in terms of favorability. (It was even less liked than Muslims and atheists, two groups that regularly meet with public opprobrium.) One of the few groups approaching the unpopularity of the Tea Party was the religious right. Both movements (which overlap heavily) might have won the staunch support of a minority of American voters, but they have also won the staunch opposition of a much larger group.

This shift has created a dilemma for Republican candidates seeking the Tea Partiers' support. Not only must Republicans toe the conservative line on fiscal issues, immigration, and national security, but Tea Party sympathizers (who compose barely a quarter of the national electorate but more than half of the Republican primary electorate) also expect them to favor a fusion of religion and politics. The problem for the Republican Party is that this fusion is unpopular among the general electorate and is becoming more so. Thus, as culture warriors fire up the Republican base, they leave independent voters cold. In contrast, more centrist candidates are attractive to the moderate middle but win only tepid support among the activists who want more God in government.

LOSING MY RELIGION

The consequences of the melding of religion and party politics extend beyond electoral politics; the commingling has also reshaped the United States' religious landscape. Just as the 1960s spurred a revival of traditional religion, the last few decades have led directly to an unprecedented turning away from organized religion, especially among younger Americans.

Consider the growth in the number of people whom sociologists call "nones," those who report no religious affiliation. Historically, this category made up a constant 5-7 percent of the American population, even during the 1960s, when religious attendance dropped. In the early 1990s, however, just as the God gap widened in politics, the percentage of nones began to shoot up. By the mid-1990s, nones made up 12 percent of the population. By 2011, they were 19 percent. In demographic terms, this shift was huge. To put the figures in context, in the two decades between the early 1970s and the early 1990s, the heyday of evangelicalism, the fraction of the population that was evangelical grew by only about five percentage points. The percentage of nones grew twice as much in the last two decades and is still climbing. Moreover, the rise is heavily concentrated among people under 30, the so-called millennial generation. To be sure, the young are always less religiously observant than their elders; people tend to become more religious when they get married, have children, and put down roots in a community (demographers call this the life-cycle effect). Yet 20-somethings in 2012 are much more likely to reject all religious affiliation than their parents and grandparents were when they were young -- 33 percent today, compared with 12 percent in the 1970s.

The millennials' movement away from organized religion has recently accelerated. Between 2006 and 2011, the fraction of nones in the population as a whole rose modestly, from 17 percent to 19 percent. Among younger Americans, however, the fraction increased approximately five times as much. Similarly, over the same five-year period, the fraction of Americans who reported never attending religious services rose by a negligible two percentage points among Americans over the age of 60 but by three times as much among those 18-29. And younger millennials are even more secular than their slightly older siblings; our 2011 survey showed that a third of Americans in their early 20s were without religion, compared with a quarter of those who were that age when we surveyed them in 2006.

The Gallup religious seismometer has signaled a plunge in religion's influence in American life, too. And in our survey, Americans of all walks of life, religious and secular, white and nonwhite, rich and poor, urban and rural, liberal and conservative, old and young, highly educated and less educated, reported the shift in about equal measure. Since we interviewed the very same people in 2006 and 2011, we can even see large numbers of individuals lowering their own estimates of religion's role in American life.

The best evidence indicates that this dramatic generational shift is primarily in reaction to the religious right. Politically moderate and progressive Americans have a general allergy to the mingling of religion and party politics. And millennials are even more sensitive to it, partly because many of them are liberal (especially on the touchstone issue of gay rights) and partly because they have only known a world in which religion and the right are intertwined. To them, "religion" means "Republican," "intolerant," and "homophobic." Since those traits do not represent their views, they do not see themselves -- or wish to be seen by their peers -- as religious.

Our data support this theory. By tracking individuals for five years, between 2006 and 2011, we found that Democrats and progressives were much more likely to become nones than were Republicans. The religious defections were concentrated specifically among those Americans who reported the greatest discomfort with religion-infused politics, regardless of their own partisan loyalties. In effect, Americans (especially young Americans) who might otherwise attend religious services are saying, "Well, if religion is just about conservative politics, then I'm outta here."

These data point to a rich irony about the emergence of the religious right. Its founders intended to bolster religion's place in the public square. In a sense, they have succeeded. Yet at the same time, in a classic demonstration of the danger of unintended consequences, the movement has pushed a growing share of the population to opt out of religion altogether.

FOR GOD'S SAKE

American religious groups have historically been distinctive in their adaptability and self-correcting tendencies. Rather than signaling the certain death of religion, our 2011 nationwide survey found hints that, feeling the heat from their too close association with partisan politics, religious leaders are beginning to pull back. Indeed, one of the most significant differences between our 2006 and our 2011 data was the drop-off in political activity within U.S. religious congregations. In 2006, 32 percent of Americans who belonged to a congregation reported hearing sermons with political content "once every month or two" or "several times a month." By 2011, that figure had fallen to 19 percent. The trend held among those of all religious traditions, in all regions of the country, among conservatives and liberals, young and old, and urban and rural. Presumably, clergy across the country have sensed what we see in the data, namely, Americans' growing aversion to blurring the lines between God and Caesar. So they have opted to stick to God.

The decrease in politicking from the pulpit will likely not have an immediate effect on the God gap. The chasm has become a fixture of the U.S. party system and is likely to persist in the short term, barring a sweeping political realignment. However, if clergy continue to retreat from politics, candidates of the religious right will have fewer opportunities to tap into church-based social networks for political mobilization. And if Republicans continue their exclusive alignment with organized religion, they will encounter ever more resistance from moderate voters, especially in the younger generation, who are in their politically formative years now and will be around for a long time.

Future historians may well see the last third of the twentieth century as an anomaly, a period in which religion and public life in the United States became too partisan for the good of either. Republican politicians facing the loss of the religiously moderate middle and pastors seeing a rapid graying of their dwindling flock are both paying a belated but serious price for the religious right's dip into politics. Beyond that, all sides -- progressive and conservative, religious and secular -- should be concerned that placing a partisan label on religion has hurt the ability of religious leaders to summon moral arguments on behalf of causes that transcend left and right. Martin Luther King, Jr.'s prophetic call for racial justice was persuasive in part because his words and deeds drew on powerful religious symbolism that could not be reduced to base partisanship. Indeed, religion has historically inspired change across the U.S. political spectrum. American public discourse -- and the country at large -- will be impoverished if religion is reduced to a mere force for partisan mobilization.

(AUTHOR BIOS: David E. Campbell is John Cardinal O'Hara, C.S.C. Associate Professor of Political Science and Director of the Rooney Center for the Study of American Democracy at the University of Notre Dame. Robert D. Putnam is Peter and Isabel Malkin Professor of Public Policy at Harvard University. This essay is adapted from the paperback edition of their book, American Grace (Simon & Schuster, 2012).)